When using the 'blown highlights' display it would be nice if it indicated straight away by using a different colour (e.g. a different shade of red, or pink or something) which parts are 'permanently' blown i.e. they went off the end of the sensor range and can't be corrected.

You can find this out by dragging exposure down to -4 and seeing bits which are still bright, but that's a bit silly. It would be nice to have this on the small previews (G screen) too. (Sometimes I take several identical shots with different exposure and it would be nice to see immediately which is the 'best' one, i.e. the brightest exposure that doesn't blow highlights, without having to examine each image in the developer view.)

You are asking to see an overlay that shows three blown channels no matter what the resulting setting of Exposure? If no matter what you do there, IF data still clips, show it with a different color? Interesting idea, could be very useful.

In fact, this is largely what the alt/option key does today on the Exposure and Recovery sliders, except that it does so on the post-processed image rather than on the raw data. Perhaps if you hold Shift and Alt/Option together...?

Where the suggestion becomes useful and interesting is a method whereby you could see that these channels clip prior to adjusting any sliders that might correct the clipping. In other words, you've got clipping that cannot be adjusted so don't bother altering the sliders. I suspect with ProPhoto RGB being used for the saturation clipping, the area where one would want this feature to apply would be only for tone clipping. You see something within the histogram that tells you, don't bother trying to adjust exposure or recovery, the highlights are blown out no matter the rendering.

Black clipping doesn't need this treatment because you should be able to clip there if you wish. But for highlight recovery, especially for those of us that expose to the right, it would be useful to see some indication that the raw data was truly 'over exposed' and clipping resulted that can't be recovered. Those may be specular highlights you don't care about. If one area on the histogram showed you the current clipping, but another somehow showed you what can't be recovered, you could decide to move onto another bracket or adjust Exposure to retain data based on the one histogram feedback and not the other.

Perhaps there is a secondary highlight clipping color besides white. White indicates the current clipping based on the sliders (mostly Exposure and Recovery). Then a secondary color (lets say gray for now) that tells you, these values are clipped no matter how you adjust the sliders.